Designing Software Architectures as Knowledge Specializations

Object-oriented methods aim at providing natural ways for decomposing (or composing) a system into (from) objects that correspond to concepts in the customer's problem domain. The identified objects are the basic building blocks of the object-oriented system to be constructed. In order not to disregard relevant objects, most methods advise software engineers to take dedicated steps such as reading books about the problem domain, interviewing customers, etc. We consider two important concerns in understanding the problem domain. First, it is very important to identify all the objects that are required for defining a consistent system, at least in its minimum configuration. Second, identified objects must serve as composable building blocks to construct robust, adaptable and reusable architecture

Data Abstraction Mechanisms in Sina/st

This paper describes a new data abstraction mechanism in an object-oriented model of computing. The data abstraction mechanism described here has been devised in the context of the design of Sina/st language. In Sina/st no language constructs have been adopted for specifying inheritance or delegation, but rather, we introduce simpler mechanisms that can support a wide range of code sharing strategies without selecting one among them as a language feature. Sina/st also provides a stronger data encapsulation than most of the existing object-oriented languages. This language has been implemented on the SUN 3 workstation using Smalltalk

A Case Study in Optimization of Resource Distribution to Cope with Unanticipated Changes in Requirements

It is a known fact that requirements change continuously, and as a consequence, it may be necessary to reschedule development activities so that the new requirements can be addressed in a costeffective manner. Unfortunately, changes in requirements cannot be specified precisely. Moreover, current software development methods do not provide explicit means to adapt development processes with respect to unanticipated changes in requirements. This article first proposes a method based on Markov Decision Theory, which determines the estimated optimal development schedule with respect to probabilistic product demands and resource constraints. Second, a tool is described that is built to support the method. Finally, some experimental results are presented on the applicability of the proposed method

Strategic Directions in Object-Oriented Programming

This paper has provided an overview of the field of object-oriented programming. After presenting a historical perspective and some major achievements in the field, four research directions were introduced: technologies integration, software components, distributed programming, and new paradigms. In general there is a need to continue research in traditional areas:\ud (1) as computer systems become more and more complex, there is a need to further develop the work on architecture and design; \ud (2) to support the development of complex systems, there is a need for better languages, environments, and tools; \ud (3) foundations in the form of the conceptual framework and other theories must be extended to enhance the means for modeling and formal analysis, as well as for understanding future computer systems

Component Composability Issues in Object-Oriented Programming

Building software from reusable components is considered important in reducing development costs. Object-oriented languages such as C++, Smalltalk and Java, however, are not capable of expressing certain aspects of applications in a composable way. Software engineers may experience difficulties in composing applications from components, for example if components implement code for multiple views, dynamic inheritance and synchronization [Aksit96]. If these aspects have to be programmed, then object-oriented languages may require a considerable amount of redefinition although this may not be intuitively necessary. To solve the composability problems, languages must be enhanced modularly without losing their basic characteristics. In addition, since more than one problem can be experienced for the same object, enhancements must be independent from each other. We have extended the conventional object-oriented model using the concept of composition-filters. Composition-filters can be attached to objects expressed for example in Smalltalk and Java. A number of different filter types have been defined, each addressing a certain concern. This paper first illustrates some practical problems and then introduces composition-filters solutions to overcome these problems

Aspect-Oriented Programming using Composition-Filters

Software engineers may experience problems in modeling certain aspects while applying object-oriented techniques [4, 10, 11]. Composition-Filters are capable of expressing various different kinds of aspects in a uniform manner. These aspects are, for example, inheritance and delegation [1] and atomic delegation [2], multiple views, dynamic inheritance and queries on objects [3], coordinated behavior and inter-object constraints [5], real-time [6] and composing real-time and synchronization together [9], synchronization [8] and distributed synchronization [7], and client-server architectures [10]

Evaluating Architecture Implementation Alternatives based on Adaptibility Concerns

Software is rarely designed for ultimate adaptability, performance or reusability but rather it is a compromise of multiple considerations. Even for a simple architecture specification, one may identify many alternative implementations. This paper makes an attempt to depict the space of implementation alternatives of architectures, and to define rules for selecting them. The applicability of this approach is illustrated by means of a simple design problem

Examples of Reusing Synchronization Code in Aspect-Oriented Programming using Composition Filters

Applying the object-oriented paradigm for the development of large and complex software systems offers several advantages, of which increased extensibility and reusability are the most prominent ones. The object-oriented model is also quite suitable for modeling concurrent systems. However, it appears that extensibility and reusability of concurrent applications is far from trivial. The problems that arise, the so-called inheritance anomalies or crosscutting aspects have been extensively studied in the literature. As a solution to the synchronization reuse problems, we present the composition-filters approach. Composition filters can express synchronization constraints and operations on objects as modular extensions. In this paper we briefly explain the composition filters approach, demonstrate its expressive power through a number of examples and show that composition filters do not suffer from the inheritance anomalies